Web or sheet edge position measurement process and device

ABSTRACT

The position of an edge of a web or sheet is measured using a photoelectric measuring device. Any edge anomalies will generate extreme edge position values. These extreme values are used together with other, more representative values, to determine an initial position of the web edge. These extreme values are then eliminated since they exceed a tolerance threshold. A revised determination of the edge location is made using the remaining position values.

FIELD OF THE INVENTION

The present invention relates to a device and a method for measuring aposition of an edge of webs or sheets by means of a photoelectricmeasuring device.

DESCRIPTION OF THE PRIOR ART

A measuring device for the photoelectric measurement of the position ofsheet edges in respect to a reference line is known from DE-OS 22 02087. Light emanating from an illumination device is received by aphotoelectrical receiver. A video signal is generated in accordance withthe position of the sheet edge which is inserted between theillumination device and the receiver.

The photoelectric receiver element consists of a plurality of individualphoto elements arranged one behind the other at short distances.

In connection with this prior art device it is disadvantageous that eventhe slightest defects or fibers at the sheet edge to be measured lead toerroneous measurements, since these defects have a direct effect on themeasurement result.

SUMMARY OF THE INVENTION

It is an object of the present invention to create a device and a methodfor measuring a position of an edge of webs or sheets by use of aphotoelectric measuring device, wherein the actual position of the edgein relation to a measuring device is determined with sufficient accuracyin spite of the presence of small defects or of fibers extending past avertical projection of the edge, for example so-called anomalies, in themeasurement area of the edge of webs or sheets.

This object is attained in accordance with the present invention bymeans of a device and a method for measuring the position of an edge ofwebs or sheets which uses a photoelectric measuring device having anillumination device and a photoelectric receiver. At least threemeasured values of a position of an edge are determined. A measuredresult is formed in a way which disregards extreme values caused by edgeanomalies.

The position of an edge of webs or sheets to be measured is detected inan advantageous manner by the device in accordance with the presentinvention at a plurality of closely adjoining points along the edge.Because of this, it is possible to neglect measured values of placeswhere edge anomalies occur. The measured values can be processed bymeans of the method in accordance with the present invention in such away that a sufficiently accurate determination of the position of theedge takes place.

In addition, it is advantageous that with a not ideally straight edge ofthe webs or sheets a virtual straight line along a considered area ofthe edge can be calculated, and that this is used as a measurement ofthe position of the edge for further processing. A sharp picture of theedge is obtained by means of the use of a light beam with parallel rays.A single illumination device for all photoelectric receivers reduces thecomponents and therefore the cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The device in accordance with the present invention and the method inaccordance with the present invention are represented in the drawingsand will be described in greater detail below. As shown in the drawings:

FIG. 1, is a schematic side elevation view of a device in accordancewith the invention taken perpendicularly in respect to thetransportation direction of the web;

FIG. 2, is a schematic side elevation view of the device in accordancewith the invention taken in the transportation direction of the web; and

FIG. 3, is a schematic top view of a plurality of photoelectricreceivers with the web.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The position of a web or sheet 1 is to be measured sheet in relation toa number of photoelectric receivers 2, with the web being bordered, atleast within the measurement area, by an edge 3 extending in the shapeof a straight line. This web or this sheet is essentiallylight-absorbing. This web or sheet 1 is preferably a paper web or asheet of paper, in particular for use in rotary printing presses, butalso be other web- or panel-shaped goods, for example sheet metal orfoils. This web or sheet 1 will be simply called web 1 hereinafter.

The edge 3 of the web 1 to be measured can have anomalies 4 in the formof, for example, small defects, tears or fibers, which can extend past aperpendicular projection of the edge 3, as seen in FIG. 3.

The web 1, which is bordered by an edge 3 with anomalies 4, is enteredinto a parallel light beam 7 while being supported on the object holder6 of an illumination device 8. The illumination device 8 essentiallyconsists of a diffusedly radiating light source 9, for example aninfrared (IR) light source 9, a diaphragm 11 and a condenser 12.

The diaphragm 11 is provided with a very narrow aperture 13, for examplea bore of a diameter of approximately 0.05 mm to 1 mm and is disposeddirectly following the IR light source 9, which radiates light of a wavelength of, for example, 750 nm. An almost punctiform or point-like IRlight source is created by means of this. The condenser 12 is located ata distance f12, which corresponds to a focal depth f12 of the condenser12, i.e. the IR light source 9 is located in the front focal point ofthe condenser 12. In the example depicted, an aspherical lens is used asthe condenser 12. The condenser 12 can also consist of several lenses,for example a combination of a concave-convex lens and one or severalaspherical lenses. In the preferred embodiment the condenser 12parallelizes the light rays 14 emanating from the punctiform IR lightsource 9 to form a light beam 7 with parallel rays.

This parallel light beam 7 can, for example, also be created by means ofa laser curtain or a laser expansion system.

In the present preferred embodiment, one light beam 7 illuminates allphotoelectrical receivers 2 together.

The light beam 7 emanates from the illuminating device 8, penetrates theobject carrier 6 as well as an IR filter 16 and impinges on thephotoelectrical receivers 2.

The task of the IR filter 16 is to eliminate daylight. The illuminatingdevice, the object carrier 6, the IR filter 16 and the photoelectricreceivers 2 are arranged along an optical axis 17.

Thus, the edge 3 or a shadow of the web 1 are represented on thephotoelectric receivers 2.

A plurality, i.e. at least three photoelectric receivers 2 are closelyarranged next to each other at a short length l, as seen in FIG. 3extending parallel with the edge 3 to be measured. The length lpreferably is less than 50 mm. For example, photoelectric receivers 2provided with a plurality of photoelements, such as a CCD field, knownper se, or several CCD line sensors (charge-coupled device), arrangedclosely next to each other, can be employed to act as the photoelectricreceivers 2. One line 18 of this CCD field of receivers 2, or of the CCDline sensor 2, can consist, for example, of 1728 measuring elementsarranged in a line 18. For example, these measuring elements can have asize of 10 μm×13 μm, and a mean distance between two measuring elementsmay be 10 μm, so that there are 100 measuring elements in on onemillimeter. In the preferred embodiment the position of the edge 3 ofthe web 1 is determined perpendicularly in respect to a measuring trackor travel direction "T" of the web 1 and in a measuring direction "M".Therefore the individual lines 18 of the CCD field of sensors 2 arearranged in a direction extending perpendiculary to the transportdirection "T" in such a way that the lines 18 in the area of the edge 3to be measured are partially covered by the web 1. The measuringdirection "M" is located parallel to a plane 5 covered by the web 1 andperpendicularly in respect to the edge 3 to be measured.

Each line 18 of the CCD field of sensors 2 is evaluated in a suitableelectronic evaluation unit 20, so that a plurality of measured values,at least three, regarding the position of the web 1 are available. Theseplurality of measured values correspond to the positions of adjoining,differentially small portions of the edge 3 of the web 1. If one orseveral anomalies 4 are now in the measuring area, the correspondingextreme values caused by these edge anomalies 4 differ from theremaining measured values. These extreme values are not considered inthe final evaluation in that an initial average value, for example, isformed and all measured values exceeding this initial average value,which determine a tolerance threshold, are not used for furthercalculations. A fresh, revised average value is formed from theremaining measured values, which then for further processing representsthe determined measurement result for the position of the edge 3.

It is also possible to determine the position of a straight linecorresponding to the position of the edge 3 by means of othermathematical processes, such as straight lines of regression,statistical frequency distribution, least error squares, etc., and touse them for further processing.

While a preferred embodiment of a device and a method for measuring aposition of a web in accordance with the present invention has been setforth fully and completely hereinabove, it will be apparent that changesin, for example, the type of web, the particular light source, the lenssystem and the like could be made without departing from the true spiritand scope of the present invention which is accordingly to be limitedonly by the following claims.

What is claimed is:
 1. A method for measuring a position of an edge of aweb by means of a photoelectric measuring device consisting of anillumination device and a photoelectric receiver, characterized in thatat least three measured values of a position of an edge are determined,that an initial average value is determined using said at least threemeasured values of a position of an edge, that extreme values of themeasured values of a position of an edge exceeding said initial averagevalue and based on anomalies of the edge are removed from furtherconsideration, and that from the remaining measured values of a positionof an edge a determined measurement result is formed whereby saidextreme values of the measured values of a position of an edge based onanomalies of the edge have no effect on said determined measurementresult.
 2. A method for determining a location of an edge of a webincluding:providing a photoelectric measuring device having a lightsource and a plurality of photoelectric receivers; directing light beamsfrom said light source onto said photoelectric receivers; positioning anedge of a web in said light beams between said light source and saidphotoelectric receivers; utilizing said photoelectric receivers togenerate a plurality of measured values, said measured valuescorresponding to adjoining, differentially small portions of said edge;determining an initial average value of said plurality of measuredvalues; using said initial average value to determine a tolerancethreshold; comparing all of said plurality of measured values to saidtolerance threshold; discarding any of said plurality of measured valuesexcluding said tolerance threshold; and using all remaining measuredvalues to determine a revised average value, said revised average valuerepresenting said location of said edge of said web.